Tube for heat exchanger

ABSTRACT

A cylindrical member of a tube for a heat exchanger is made of a pair of flat plate portions, and a pair of curved portions for connecting the pair of flat plate portions to each other. One of the pair of curved portions constructs a bonded portion in which an outer wall portion and an inner wall portion are bonded to each by brazing in a state where the outer wall portion and the inner wall portion overlap each other. The inner wall portion has a portion opposite to the outer wall portion put into close contact with the outer wall portion and is bonded to the one flat plate portion in a state where a tip end portion of the inner wall portion opposite to the one flat plate portion is separated from the one flat plate portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2010-252807filed on Nov. 11, 2010, the contents of which are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to a tube for a heat exchanger, which canbe usefully applied to, for example, a radiator of an automobile or thelike.

BACKGROUND ART

A flat tube formed by bending a plate-shaped part (for example, a metalplate) has been known as a tube for a heat exchanger. These flat tubesand corrugated fins are alternately stacked on each other to therebyform a heat exchange core, and a tank and piping for introducing a heatexchange medium are coupled to the heat exchange core, so that a heatexchanger is constructed.

This kind of flat tube is made of: a pair of flat plate portions whichare opposite to each other with a given gap between them in a minorradius direction; a curved portion which is curved and connected to eachof the pair of flat plate portions on one side in a major radiusdirection to thereby connect the pair of flat plate portions to eachother; and a bonded portion in which the respective flat plate portionsare bonded to each other on the other end side in the major radiusdirection.

In the bonded portion of the flat tube, an outer wall portion extendingfrom an end portion of one of the flat plate portions and constructingan outer wall of the flat tube is bonded and brazed to an inner wallportion extending from an one end portion of the other of the flat plateportions and constructing an inner wall of the flat tube in anoverlapping state. In this case, if a brazing material is not suitablyintroduced into the bonded portion in the flat tube, a fluid flowing inthe flat tube is likely to leak to the outside because of faultybrazing.

In contrast to this, in order to improve the brazing performance of abonded portion in the flat tube, for example, in patent document 1 isproposed a construction in which an end portion of an inner wall portionpositioned inside the bonded portion is separated from a wall face of anouter wall portion positioned outside the bonded portion.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP-A-2001-137989

If a plate-shaped part of a tube for a heat exchanger is varied inlength, width, and strength, a position of an end portion of an innerwall portion may be shifted by a compressive force applied in a minorradius direction of the flat tube when the flat tubes and the corrugatedfins are alternately stacked on each other to thereby form a heatexchange core.

At this time, as in the case of the patent document 1, in theconstruction in which the end portion on the inner wall portionpositioned inside the bonded portion is separated from the wall face ofthe outer wall portion positioned outside the bonded portion, when theposition of the end position of the inner wall portion is shifted, abond shape in the bonded portion is changed to reduce adhesion betweenthe outer wall portion and the inner wall portion. As a result, abrazing performance in the flat tube may be unstable in some cases.

SUMMARY OF THE INVENTION

In view of the matters described above, an object of the presentinvention is to improve a brazing performance in a bonded portion of atube for a heat exchanger.

According to an aspect of the present disclosure, a tube for a heatexchanger includes a cylindrical member in which a heat exchange mediumflows and which is made of a plate-shaped part having a flow passagesection formed in a flat shape. The flow passage section beingorthogonal to a direction in which the heat exchange medium flows. Thecylindrical member includes a pair of flat plate portions opposite toeach other in parallel in a minor radius direction of the flow passagesection, and a pair of curved portions opposite to each other in a majorradius direction of the flow passage section and for connecting the pairof flat plate portions to each other. One curved portion of the pair ofcurved portions constructs a bonded portion in which an outer wallportion, which extends from an end portion of one flat plate portion inthe pair of flat plate portions and constructs an outer wall of thecylindrical member, and an inner wall portion, which extends from an endportion of other flat plate portion in the pair of flat plate portionsand constructs an inner wall of the cylindrical member, are bonded andbrazed to each other in a state where the outer wall portion and theinner wall portion overlap each other. Furthermore, the inner wallportion has an opposite portion opposite to the outer wall portion putinto close contact with the outer wall portion, and is bonded to the oneflat plate portion in a state where a tip end portion opposite to theone flat plate portion is separated from the one flat plate portion.

According to the present disclosure, when a tube for a heat exchanger isassembled, even if a compressive force is applied to the tube in a minorradius direction of the tube, the position of the tip end positionopposite to the flat plate portion in the inner wall portion is onlyshifted and adhesion between the inner wall portion and the outer wallportion can be held. As a result, the brazing performance in the bondedportion in the tube for a heat exchanger can be improved.

For example, each of the pair of curved portions may be curved in theshape of an arc. According to this, when the compressive force isapplied to the tube in a minor radius direction of a flow passagesection, it is possible to prevent the bonded portion from being buckledand deformed. Hence, the brazing performance of the bonded portion inthe tube for a heat exchanger can be improved.

Further, the tube for a heat exchanger may be constructed in such a waythat a portion opposite to the outer wall portion in the inner wallportion is formed in a continuously curved face and that the outer wallportion is extended along the continuously curved face of the inner wallportion.

Still further, the inner wall portion may have an extended portionextended from a portion opposite to the outer wall portion to the othercurved portion side. The extended portion may have a portion opposite tothe flat plate portions formed in a wavy shape in such a way that theportion functions as an inner fin and further may have a portionopposite to an inner wall face of the other curved portion extendedalong and put into close contact with an inner peripheral face of theother curved portion and is bonded to the flat plate portion in a statewhere a tip end portion opposite to the flat plate portion on the othercurved portion side is separated from the flat plate portion.

In this way, even in a case where the extended portion in the inner wallportion is constructed as the inner fin, even if the compressive forceis applied to the tube in the minor radius direction when the tube for aheat exchanger is assembled, the position of the tip end portionopposite to the flat plate portion in the inner wall portion is onlyshifted and adhesion between the inner wall and the outer wall portionand adhesion between the extended portion in the inner wall portion andthe inner peripheral face of the other curved portion can be held. As aresult, the brazing performance in the bonded portion in the tube for aheat exchanger can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned or other objects, constructions, and advantages inthe present invention will be made clearer by the following detaileddescriptions with reference to the following drawings.

FIG. 1 is a front view of a radiator according to a first embodiment.

FIG. 2( a) is a section view to show a flow passage section of a flattube according to the first embodiment, and FIG. 2( b) is an enlargedview of a portion A in FIG. 2( a).

FIG. 3( a) and FIG. 3( b) are illustrations to illustrate a process formanufacturing the radiator according to the first embodiment.

FIG. 4 is an illustration to illustrate a difference between acylindrical member according to the first embodiment and a cylindricalmember of a related art.

FIGS. 5( a), 5(b), and 5(c) are illustrations to illustrate a differencebetween the cylindrical member according to the first embodiment and thecylindrical member in the related art.

FIGS. 6( a) and 6(b) are illustrations to illustrate a differencebetween the cylindrical member according to the first embodiment and thecylindrical member in the related art.

FIGS. 7( a) and 7(b) are illustrations to illustrate the cylindricalmember according to the first embodiment.

FIG. 8( a) is a section view to show a flow passage section of a flattube according to a second embodiment, and FIG. 8( b) is an enlargedview of a portion B in FIG. 8( a).

FIG. 9 is a partial section view to show a flow passage section of aflat tube according to another embodiment.

FIG. 10 is a partial section view to show a flow passage section of aflat tube according to further another embodiment.

FIG. 11 is a partial section view to show a flow passage section of aflat tube according to further another embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described onthe basis of the drawings. In the respective embodiments to be describedbelow, parts equal or equivalent to each other are denoted by the samereference numerals in the drawings.

First Embodiment

A first embodiment of the present invention will be described on thebasis of FIG. 1 to FIG. 7. FIG. 1 is a front view of a radiator 1according to the present embodiment.

In the present embodiment, a flat tube (tube for a heat exchanger) 2 isapplied to a radiator 1 for exchanging heat between an engine coolingwater (heat exchange medium) for cooling a vehicle engine (internalcombustion engine) and air (atmosphere).

The flat tube 2 in FIG. 1 is a tube in which the engine cooling waterflows. The flat tube 2 is formed in a flat shape in such a way that adirection in which air flows (direction vertical to a plane of paper ofFIG. 1) is aligned with a major radius direction. Further, a pluralnumber of flat tubes 2 are arranged parallel to each other in a verticaldirection in FIG. 1 in such a way that its longitudinal direction isaligned with a horizontal direction in FIG. 1. A detailed description ofthe flat tube 2 will be provided later.

An outer fin (corrugated fin) 3 formed in a wavy shape is bonded to bothoutside surfaces of a plane, which is parallel to the direction in whichthe air flows, of the flat tube 2. The outer fin 3 increases a heattransfer area to the air to thereby accelerate a heat exchange betweenthe engine cooling water and the air. Hereinafter, a heat exchange corepart 4, which is constructed of the flat tubes 2 and the outer fins 3,is abbreviated simply as a core part 4.

A header tank 5 extends in a direction orthogonal to a longitudinaldirection of the flat tube 2 (in an up and down direction in FIG. 1) atan end portion in the longitudinal direction of the flat tube 2 (endportion in a left and right direction in FIG. 1) and communicates withthe plural number of flat tubes 2.

The header tank 5 includes a core plate 5 a having the tubes 2 insertedthereinto and bonded thereto and a tank main body 5 b constructing atank interior space together with the core plate 5 a. The core part 4has inserts 6 provided on both end portions thereof, the inserts 6extending nearly parallel to the longitudinal direction of the flat tube2 and reinforcing the core part 4.

In the present embodiment, the flat tube 2, the outer fin 3, the coreplate 5 a, and the tank main body 5 b are made of metal (for example,aluminum alloy). The surface of the flat tube 2 and a bonded portion inthe core plate 5 a and the tank main body 5 b are coated with a brazingmaterial.

Next, the construction of the flat tube 2 of the present embodiment willbe described on the basis of FIG. 2( a) and FIG. 2( b). FIG. 2( a) andFIG. 2( b) are section views to show a flow passage section of the flattube 2 of the present embodiment. FIG. 2( a) shows an entire flowpassage section of the flat tube 2 and FIG. 2( b) shows a partialenlarged view of a portion A in FIG. 2( a).

As shown in FIG. 2( a) and FIG. 2( b), the flat tube 2 of the presentembodiment is constructed of a cylindrical member 20 in which a flowpassage section orthogonal to a direction in which the engine coolingwater flows is formed in a flat shape. The cylindrical member 20 isformed by bending a metal plate (plate-shaped part).

The cylindrical member 20 formed in the flat shape is constructed of apair of plate portions 21, 22 opposite to each other in parallel in aminor radius direction (in the up and down direction of a plane ofpaper) and a pair of curved portions 23, 24 each of which is curvedoutward in the shape of a circular arc in a major radius direction (inthe left and right direction of the plane of paper). In the presentembodiment, a flat plate portion on an upper side in the drawing isreferred to as a first flat plate portion 21 and a flat plate portion ona lower side in the drawing is referred to as a second flat plateportion 22, whereas one curved portion (on a left side in the drawing)is referred to as a first curved portion 23 and the other curved portion(on a right side in the drawing) is referred to as a second curvedportion 24.

The first curved portion 23 is a curved portion of connecting therespective flat plate portions to each other and constructs a wallportion of connecting an end portion on one end side (on the left sidein FIG. 2) of the first flat plate portion 21 to an end portion on oneend side (on the left side in FIG. 2) of the second flat plate portion22.

The second curved portion 24 is constructed of an outer wall portion241, which extends from an end portion on the other end side (on theright side) of the first flat plate portion 21 and constructs an outerwall of the cylindrical member 20, and an inner wall portion 242, whichextends from an end portion on the other end side (on the right side) ofthe second flat plate portion 22 and constructs an inner wall of thecylindrical member 20. The second curved portion 24 constructs a bondedportion (double wall) in which the inner wall face of the outer wallportion 241 is bonded by brazing to a portion of the outer wall face ofthe inner wall portion 242 in an overlapping state.

The inner wall portion 242 in the second curved portion 24 has a portionopposite to the outer wall portion 241 (outer wall face) formed in acontinuously curved face. In other words, the inner wall portion 242 ofthe present embodiment does not have a depressed portion (transitportion) for receiving an end portion of the outer wall portion 241.

On the other hand, the outer wall portion 241 is extended along andbonded to the continuously curved face (outer wall face) of the innerwall portion 242. In other words, the outer wall portion 241 is bondedto the continuously curved face of the inner wall portion 242 in a closecontact state with the outer wall face of the inner wall portion 242.

Further, the inner wall portion 242 has an extended portion 243 extendedfrom a portion opposite to the outer wall portion 241 and is bonded tothe outer wall portion 241 in a state where a tip end portion 244 of theextended portion 243 is separated from a wall face of the first flatplate portion 21. The extended portion 243 is a portion opposite to thefirst flat plate portion 21 in the inner wall portion 242 and isconstructed in such a way as to be continuously curved from a portionopposite to the outer wall portion 241 in the inner wall portion 242.The extended portion 243 is extended from a boundary (an end position EDof the first flat plate portion 21) between the first flat plate portion21 and the outer wall portion 241 in the major radius direction of thecylindrical member 20 and is arranged at a position opposite to aportion on the first flat plate portion 21 side of the cylindricalmember 20. In the drawing, the end position ED shows an end position ofthe first flat plate portion 23, that is, a position of the boundarybetween the first flat plate 21 and the outer wall portion 241. Theextended portion 243 is extended from the ED position to the tip endportion 244 side and is arranged opposite to the first flat plateportion 21. In the present embodiment, as shown in FIG. 2( b), a faceopposite to the first flat plate portion 21 in the extended portion 243is constructed of a bonded face portion bonded to a flat face of thefirst flat plate portion 21 and a separated face portion separated fromthe first flat plate portion 21 on the tip end portion 244 side.

Next, a method for manufacturing the radiator 1 will be simply describedby the use of FIGS. 3( a) and 3(b). FIGS. 3( a) and 3(b) areillustrations to illustrate a process for manufacturing the radiator 1.

First, as shown in FIG. 2, a metal plate (plate-shaped part) havinggiven dimensions is bent nearly at a central portion by a roll formingor the like and then both end portions of the bent metal plate areoverlaid on each other in close contact to thereby form the cylindricalmember 20 of the flat tube 2.

The flat tubes 2 and the outer fins 3 are alternately stacked on eachother to thereby assemble the core part 4 and the core part 4 is furtherassembled with the header tank 5. Then, these parts are prevented frommoving by a jig as required and are kept in a temporary assemblingstate. When the core part 4 is assembled, in order to suitably put theflat tubes 2 and the outer fins 3 into close contact with each other,the flat tubes 2 and the outer fins 3 are temporarily fixed to eachother by wires 7 (see FIG. 3( a)) or a clamp 8 (see FIG. 3( b)) in astate where a load is applied to the flat tubes 2 and the outer fins 3in a staking direction.

Thereafter, an assembly kept in the temporary assembling state is heatedto a temperature not lower than a melting point of the brazing materialcoated on the respective parts in a vacuum heating furnace or a heatingfurnace in an inert gas atmosphere, so that the brazing material ismelted and the respective to-be-bonded parts of the assembly areintegrally brazed to each other.

Here, the flat tube 2 has a compressive force applied thereto in adirection in which the first flat plate portion 21 and the second flatplate portion 22 come closer to each other (in a minor radius directionof the cylindrical member 20) by the load applied thereto by the jigwhen the core part 4 is assembled or by the outer fin 3 being stackedthereon. In the present embodiment, the flat tube 2 is constructed ofone metal plate (plate-shaped part), so that if the plate-shaped part isvaried in length, width, and strength, when the compressive force isapplied to the flat tube 2 in the minor radius direction of thecylindrical member 20, the position of the tip end portion 244 of theinner wall portion 242 in the second curved portion 24 of thecylindrical member 20 is shifted.

At this time, in a structure in which the tip end portion 244 of theinner wall portion 242 in the second curved portion 24 is not extendedto a position opposite to the first flat plate portion 21 but in whichthe tip end portion 244 of the inner wall portion 242 abuts on the outerwall portion 241, when the compressive force is applied to the flat tube2 as shown in FIG. 5( a), the tip end portion 244 of the inner wallportion 242 can be shifted in some cases in a direction to push up thefirst flat plate portion 21 or in a direction to push out the outer wallportion 241, as shown in FIG. 5( b) and FIG. 5( c).

Further, even if the tip end portion 244 of the inner wall portion 242in the second curved portion 24 is extended to the position opposite tothe first flat plate portion 21 as in the case of the cylindrical member20 of the present embodiment, in a structure in which the tip endportion 244 of the inner wall portion 242 abuts on the first flat plateportion 21, when the compressive force is applied to the flat tube 2 asshown in FIG. 4, the tip end portion 244 of the inner wall portion 242can be shifted in some cases in a direction to push up the first flatplate portion 21.

Still further, in a structure in which the tip end portion 244 of theinner wall portion 242 in the second curved portion 24 is not extendedto the position opposite to the first flat plate portion 21 but in whichthe tip end portion 244 of the inner wall portion 242 is separated fromthe outer wall portion 241, as shown in FIG. 6( b) and FIG. 6( c), whenthe compressive force is applied to the flat tube 2, the tip end portion244 of the inner wall portion 242 can be shifted in some cases into agap between the outer wall portion 241 and the inner wall portion 242.FIGS. 4 to 6 are illustrations to illustrate a difference between thecylindrical member 20 of the present embodiment and a cylindrical memberof the related art.

In these structures, when the position of the tip end portion 244 of theinner wall portion 242 is shifted, the shape of close contact betweenthe outer wall portion 241 and the inner wall portion 242 is varied toeasily cause the gap between the outer wall portion 241 and the innerwall portion 242, which hence makes a brazing performance at the bondedportion unstable. This presents a problem of causing a liquid leak andan internal corrosion in the bonded portion of the flat tube 2.

In contrast to this, the present embodiment employs a structure in whichthe tip end portion 244 of the inner wall portion 242 in the secondcurved portion 24 is extended to the position opposite to the first flatplate portion 21 and in which the tip end portion 244 of the inner wallportion 242 is separated from the first flat plate portion 21.Specifically, as shown in FIG. 2( b), a face opposite to the first flatplate portion 21 in the extended portion 243 is constructed of a bondedface portion bonded to a flat face of the first flat plate portion 21and a separated face portion separated from the first flat plate portion21 on the tip end portion 244 side.

In the flat tube 2 having the structure like this, even if thecompressive force is applied to the flat tube 2 as shown in FIG. 7( b),the position of the tip end portion 244 of the inner wall portion 242 isshifted in a state in which the shape of close contact between the outerwall portion 241 and a portion opposite to the outer wall portion 241 inthe inner wall portion 242 is held.

Thus, this makes it difficult to cause a gap between the outer wallportion 241 and the inner wall portion 242 and hence can improve thebrazing performance in the flat tube 2. As a result, it is possible toeffectively prevent the liquid leak and the internal corrosion frombeing caused at the bonded portion of the flat tube 2.

Second Embodiment

Next, a second embodiment of the present invention will be described onthe basis of FIG. 8( a) and FIG. 8( b). Here, FIG. 8( a) and FIG. 8( b)are section views to show a flow passage section of a flat tube 2 of thepresent embodiment. FIG. 8( a) shows an entire flow passage section ofthe flat tube 2 and FIG. 8( b) shows a partial enlarged view of aportion B in FIG. 8( a). In the present embodiment, the descriptions ofparts similar to or equivalent to those in the first embodiment will beomitted or simplified.

The flat tube 2 of the present embodiment has an extended portion 243 inwhich an inner wall portion 242 is extended from a portion opposite toan outer wall portion 241 to a first curved portion 23. In the extendedportion 243, a portion (fin portion 243 a) opposite to the respectiveflat plate portions 21, 22 in a minor radius direction of the flat tube2 is formed in a wavy shape in such a way as to function as an inner finfor increasing a heat transfer area for an engine cooling water. The finportion 243 a has its peak portions of the wavy shape formed in such away as to be in contact with the respective flat plate portions 21, 22.

Further, the extended portion 243 has a portion (fin end portion 243 b)opposite to an inner wall face of the first curved portion 23 extendedalong and put into close contact with an inner peripheral face of thefirst curved portion 23 and is bonded to the second flat plate 22 in astate where a tip end portion 244 opposite to the second flat plateportion 22 on the first curved portion 23 side is separated from thesecond flat plate portion 22. As shown in FIG. 8( b), the extendedportion 243 on the tip end portion 244 side is bonded to the second flatplate portion 22 with the tip end portion 244 separated from the secondflat plate portion 22.

According to the construction of the present embodiment, the extendedportion 243 is bonded to the second flat plate portion 22 in a statewhere the tip end portion 244 is separated from the second flat plateportion 22, so that even if a compressive force is applied to the flattube 2 in a minor radius direction of the flat tube 2, the position ofan end portion of the second flat plate portion 22 is only shifted andthe inner wall portion 242 can be bonded to the outer wall portion 241and the extended portion 243 can be bonded to the second flat plateportion 22 in a state where the close contact between the inner wallportion 242 and the outer wall portion 241 and the close contact betweenthe extended portion 243 in the inner wall portion 242 and the innerperipheral face of the first curved portion 23 are held. As a result,the brazing performance at the bonded portion in the flat tube 2 can beimproved.

Other Embodiments

Up to this point, the embodiments of the present invention have beendescribed but the present invention is not limited to these embodiments.Unless the present invention does not depart from the scope described inthe respective claims, the present invention is not limited by the wordsand phrases described in the respective claims but can cover also ascope easily replaced from the claims by a person skilled in the art andcan have modifications added thereto as required, the modificationsbeing based on knowledge usually possessed by the person skilled in theart. For example, the present invention can be variously modified as inthe following manner.

(1) In the respective embodiments described above, the inner wallportion 242 in the second curved portion 24 has a portion (outer wallface) opposite to the outer wall portion 241 formed by the continuouslycurved face, but the present invention is not limited to this. Forexample, as shown in FIG. 9, the invention may employ a construction inwhich the inner wall portion 242 has a depressed portion 242 a forreceiving an end portion of the outer wall portion 241.

(2) In the first embodiment described above, the extended portion 243 inthe inner wall portion 242 is constructed in such a way as to becontinuously curved from the portion opposite to the outer wall portion241 in the inner wall portion 242, but the present invention is notlimited to this. For example, as shown in FIG. 10, the present inventionmay employ a construction in which the extended portion 243 in the innerwall portion 242 is bent from a portion opposite to the outer wallportion 241 in the inner wall portion 242.

(3) In the first embodiment described above, the tip end portion 244 ofthe extended portion 243 in the inner wall portion 242 is separated fromthe first flat plate portion 21 on the second curved portion 24 side inthe first flat plate portion 21, but the present invention is notlimited to this. For example, as shown in FIG. 11, the tip end portion244 of the extended portion 243 in the inner wall portion 242 may beseparated from the first flat plate portion 21 on the first curvedportion 23 side in the first flat plate portion 21. Further, the presentinvention may employ a construction in which the extended portion 243 isbent in the minor radius direction between the first flat plate portion21 and the second flat plate portion 22 to thereby form a bent portion243 c and in which the bent portion 243 c is made to abut on the firstflat plate portion 21 and the second flat portion 22 to thereby functionas a support part for supporting the first flat plate portion 21 and thesecond flat portion 22.

(4) In the respective embodiments described above, the first curvedportion 23 and the second curved portion 24 are formed in the shape ofthe circular arc. However, the shape of the first curved portion 23 andthe shape of the second curved portion 24 are not limited to in theshape of the circular arc but may be a shape of a combination of circleshaving different radiuses of curvature. Further, the shape of the firstcurved portion 23 and the shape of the second curved portion 24 may be ashape of a combination of a curved face and a flat face parallel to theminor radius direction of the cylindrical member 20.

(5) In the respective embodiments described above have been describedthe examples in which the tube for a heat exchanger according to thepresent invention is applied to the radiator 1. However, the presentinvention is not limited to this but can be applied to various kinds ofheat exchangers such as a heater core unit, an evaporator, and acondenser.

1. A tube for a heat exchanger, comprising a cylindrical member in whicha heat exchange medium flows and which is made of a plate-shaped parthaving a flow passage section formed in a flat shape, the flow passagesection being orthogonal to a direction in which the heat exchangemedium flows, wherein the cylindrical member includes a pair of flatplate portions opposite to each other in parallel in a minor radiusdirection of the flow passage section, and a pair of curved portionsopposite to each other in a major radius direction of the flow passagesection and for connecting the pair of flat plate portions to eachother, one curved portion of the pair of curved portions constructs abonded portion in which an outer wall portion, which extends from an endportion of one flat plate portion in the pair of flat plate portions andconstructs an outer wall of the cylindrical member, and an inner wallportion, which extends from an end portion of other flat plate portionin the pair of flat plate portions and constructs an inner wall of thecylindrical member, are bonded by brazing to each other in a state wherethe outer wall portion and the inner wall portion overlap with eachother, the inner wall portion has an opposite portion opposite to theouter wall portion put into close contact with the outer wall portion,and is bonded to the one flat plate portion in a state where a tip endportion of the inner wall portion opposite to the one flat plate portionis separated from the one flat plate portion, and the inner wall portionhas an extended portion extended from a boundary between the first flatplate portion and the outer wall portion, to a side of the other curvedportion, and the tip end portion separated from the one flat plateportion is positioned inside of the boundary in the major radiusdirection and is opposite to the one flat portion.
 2. The tube for aheat exchanger according to claim 1, wherein each of the pair of curvedportions is curved in a shape of an arc.
 3. The tube for a heatexchanger according to claim 1, wherein the inner wall portion has acontinuously curved face opposite to the outer wall portion, and theouter wall portion is extended along and bonded to the continuouslycurved face of the inner wall portion.
 4. The tube for a heat exchangeraccording to claim 1, wherein the extended portion has a wavy-shapedportion that is opposite to the pair of flat plate portions and isformed in a wavy shape in such a way that the wavy-shaped portionfunctions as an inner fin, and further has a portion opposite to aninner wall face of the other curved portion extended along and put intoclose contact with the inner wall face of the other curved portion, andthe extended portion is bonded to the flat plate portion in a statewhere the tip end portion opposite to the flat plate portion on a sideof the other curved portion is separated from the flat plate portion. 5.The tube for a heat exchanger according to claim 1, wherein a faceopposite to the flat plate portion in the extended portion isconstructed of a bonded face portion bonded to a flat face of the flatplate portion and a separated face portion separated from the flat plateportion at the tip end portion.
 6. The tube for a heat exchangeraccording to claim 1, wherein the inner wall portion has a contact facecontacting the outer wall portion, and the contact face of the innerwall portion has a shape along the outer wall portion.
 7. The tube for aheat exchanger according to claim 1, wherein the extended portion of theinner wall portion has a contact face contacting a flat shape of the oneflat plate portion.